MECHANICAL DESIGN

FIG. 3-Block diagram of the console and line unit

FIG, 4-Block diagram of the console processor PWB

Left of console PCB

FIG, 5-Console processor PWB

Console Main Firmware

The control program for the console processor consists of a number of routines for controlling the operation of the console peripheral units. 

The routines are known as the Link - handler, 

the VDU handler, the keyboard handler, 

a bleep routine and a 

flash routine. 

These routines are run periodically, under the control of the scheduler; an exception is the link handler, which runs on an interrupt basis. Fig. 6 shows how these routines relate to the console peripherals and indicate the main flow of data through the console. The control program also contains a memory-testing routine which periodically exercises the console RAM.

When a call is made into the PABX, the central equipment processor scans and controls the line interface being used. If the call has to be directed to the console (for example, an incoming exchange line call), the central equipment processor causes the console line unit to transmit a 3 byte message over the signalling link to the console. The link handler ensures that the data received is forwarded to the other routines to enable appropriate action to be taken.

As with the central equipment unit, enhanced facilities for the console can be introduced in the future by making appropriate changes to the control program. The facility is provided for reprogramming the PROM devices (after erasure under ultra-violet light) without removing them from the processor PWB.

The control program for the console does not vary with different sizes of PABX. Information regarding system configuration is transmitted to the console by the central equipment unit and stored in the RAM on the processor PWB. This occurs each time the processor in the central equipment or console is first brought into use; for example, when the console is first powered. Thus, a console recovered from one customer's PABX can immediately be re-used at another Monarch 120 site.

VISUAL DISPLAY UNIT electroluminescent, (later LCD was used)

A DC electroluminescent (DCEL) panel is used for the console VDU. This panel gives an alphanumeric display in 4 rows of 16 characters, each character being formed from a 5 x 7 dot matrix. The display area is 76 mrn wide by 34 111m high, each character is approximately 3 mrn wide and 4 mm high. The DCEL panel is supplied by GEC Hirst Research Centre and Phosphor Products Ltd.

The front viewing panel of the VDU consists of a glass plate, on the rear face of which are deposited layers of material (including phosphor) which form an electrically-conducting grid pattern. The rear face of the plate is protected from atmospheric moisture by further glass encapsulation.

The panel is clamped onto a PWB, and electrical connexions to the conducting grid are made via two elastomeric connectors positioned along the top and bottom edges of the panel. This PWB is also used to mount 5 LEDs, which indicate alarm conditions and system status (see Fig. 8(0». The drive circuitry for the VDU is accommodated on a second PWB (see Fig. 8(b» which connects directly with the PWB on which the panel is mounted.

When a potential (above a certain threshold value) is applied between a horizontal row and a vertical column on the conducting grid, the phosphor dot at their point of inter- section will emit light; the VDU drive circuitry applies a positive 120 V potential to the row, and earth potential to the column. Tn the idle condition, a positive 60 V potential is applied to both row and column and the dot is not illuminated. The threshold potential required to illuminate a dot is approximately 70 V.

A block diagram of the VDU drive circuit is shown in Fig. 9.

To drive all the dots on the VDU (2240 in total) it is necessary to use multiplexing techniques. The columns are continually scanned such that each is selected in turn and driven from +60 V potential. The VDU (80 columns) is scanned at a rate of 600 Hz; thus, within each scan period (1'67 rns), each column is selected for 21 us, During this period, a + 120 V potential is applied to those rows containing the dots to be illuminated. (The remaining dots in the selected column have a +60 V potential on the row, but this is below the threshold required to illuminate them.)

1984 Hitatchi LM017 Based VDU

32 character  x 2 line  LCD display

LCD VDU Driver Board

(a) Display PWB

(b) VDU drive circuit PWB

FIG. 8-Visual display unit PWBs

FIG. 9-Block diagram of the VDU drive circuit

When the console processor responds to an event such as a key operation or an incoming link message from the central equipment unit, one of the processor's activities is the control of the VDU. The VDU has its own complementary metal- oxide semiconductor (CMOS) static RAM, in which there is stored one bit of data corresponding to each dot on the VDU. To display a message on the VDU the processor writes data into the RAM, which effectively becomes a memory map of the display.

To prevent corrupted data being displayed continually, the processor completely refreshes the VDU RAM once every second. This is done both when the VDU is clear and when a message is being displayed.

An uncommitted logic array (ULA) uses a 1.536 MHz clock waveform, sent from the processor PWB, to derive all the timing signals required for the RAM, row drive circuit and column drive circuit. The ULA also controls access to the RAM, which has to be shared between write periods from the the processor and read periods from the row drive circuit. If, for example, the ULA has just caused the column drive circuit to select the first column on the VDU then, within the 21 fLs selection period, the ULA will control the RAM addressing so that the appropriate data (28 bits) is read from the RAM and latched into the row drive circuit, which then translates the logical levels zero and aile to the +60 V and + 120 V potentials to be applied to the panel. The appropriate dots in the selected column will then be illuminated.

The row drivers are hybrid devices; each 14-pin single-in- line package contains circuitry to drive 4 rows of dots, there- fore 7 hybrid packages are required for the whole VDU.

After the dots have been illuminated for a while, the ULA sends a signal to the row drive circuit to clear the + 120 V potential and restore the -1-60 V potential for all the rows. The period of time in which this action is initiated can be varied by setting a switch on the VDU drive circuit PWB, thus allowing the brightness of the display to be controlled; the period is, typically, 8 us, giving a dot duty cycle of approximately 0·5 %.

After the 21 micro second column select period has elapsed, the ULA will cause the column drive circuit to select the second column on the VDU and the whole process is repeated. The ULA addresses a different area of the RAM, holding the data corresponding to the dots in the second column. This cycle is repeated 80 times for each complete scan of the VDU.

The light output from a phosphor dot decays to approximately 15 % of its maximum before the driving potential of + 120 V is re-applied (after I· 67 ms), However, the display appears completely free of flicker because of the high scan rate used.

The light emitted by the panel is yellow in colour, and is closely matched to that part of the spectrum in which the human eye has its maximum sensitivity. A grey filter plate is provided in front of the VDU; this plate has an anti-reflective finish on the front surface and also serves to improve the contrast ratio of the display. The maximum brightness of the panel could be 180 candela/m? at 120 V, but the brightness is set below this value on the VDU drive PWB. The brightness of the panel display is further reduced by transmission losses through the VDU filter plate; in this way, the brightness apparent to the operator is about 70 candela/rn-.

The operator's speech circuit consists of a 20-pin dual-in- line thick-film hybrid package (containing an array of resistors, CMOS bilateral switches and operational amplifiers) and a few discrete components. The CMOS switches are controlled by the console processor and are used to connect either or both of the 4-wire circuits to the transmitter and receiver in the handset under the control of the SPEAK 1, SPEAK 2 and JOIN keys, thus providing the normal operator facility of call- splitting and joining. Another CMOS switch is used to select a different gain setting for the operational amplifier in the path to the handset receiver, under the control of the VOLUME key. Thus the operator can increase the loudness of calls by 6 dB, if required. The hybrid package contains a feedback path between transmitter and receiver connexions to provide the correct level of sidetone on the handset.

Intrusion tone is generated on the miscellaneous circuits PWB and, when appropriate, this tone is injected into a 3- party call via the transmitter input to the speech circuit hybrid.

CONSOLE FACILITIES

One of the major features of the Monarch 120 system is the wider range of extension and operator facilities offered in comparison with existing small PABXs3. The Monarch 120 operator's console provides 'key-per-function' working, rather than 'key-per-line' (as used on many other systems), and allows simple functional control of the PABX for both experienced and inexperienced operators. This feature is important at smaller installations where the level of telephone traffic is relatively low and where the operator may also have other duties as a receptionist or secretary.

Lines incoming to the PABX (exchange lines and inter- PBX circuits) can be arranged in up to 4 separate groups, as defined in the system database. Successive calls within each group are queued automatically in order of arrival, and a faster LED flash rate indicates that more than one call is awaiting answer. The operator can therefore choose which call queue will be handled, by operating the appropriate INCOMI G GROUP key; the VDU then shows the identity of the line connected.

To extend the call inwards, the operator merely keys the extension number, which is also shown on the VDU together with the status of the line; for example, the word RINGING is indicated on the VDU. In this case, the operator can either wait to announce the call to the extension or can operate the WITHDRAW key, leaving the incoming caller receiving ringing tone. If the call remains unanswered for 30 s, the call reverts automatically to the console, where it is placed on the "WAIT- ING RETURN" queue.

If the extension being called is busy, the VDU shows BUSY, ACTION? In this case, the operator can redirect the call or use the INTRUDE key to break into the existing call (warn tone is introduced at this stage) to announce that a call is waiting. Alternatively, the incoming call could be put into a "HOLD" status until further attempts to connect the call prove success- ful; in this case, the legend HI is flashed in one corner of the VDU to remind the operator that one call has been held on the console. More than one call can be held at a time, in which case the number of calls held is indicated by H2, H3 etc. on the VDU. The RETRIEVE key is used when the operator wishes to speak to a held call; successive operation of the HOLD and RETRIEVE keys selects the held calls on a cyclic basis.

Calls to the operator from PABX extensions are placed on the ASSIST queue; those from PABX extensions already engaged on a call and making an enquiry to the operator are placed on the "CALL-IN" queue.

If the party on an "INCOMING GROUP" call states that subsequent calls to other extensions will be required, then the operator can set up a "SERIES CALL". On conclusion of the first call, the incoming call is placed on the "SERIES RETUR " queue on the console, so that the operator can set up the next extension call.

In answering calls at the console, the operator can choose to speak privately to either party involved, by operating the SPEAK I or SPEAK 2 key, and then restore a 3-way connexion by using the JOIN key. The YOU shows the speech connexion status of both parties on the call. The operator can also increase the loudness of a call to the console by operating the VOLUME key; when there is no call being handled, this key is used to alter the volume of the audible tones given to indicate incoming calls and confirm key operation (these can be individually adjusted).

Outgoing exchange and inter-PBX lines are also arranged in up to 4 outgoing groups, which are defined in the system database. If more than 4 groups are required, then access to these can be made using a digit code on the keypad. When necessary, the TRU K SELECT key (followed by a digit code) can be used to seize a particular line within a group; this would normally be done whilst trying to identify a faulty line.

If an outgoing group call does not mature, a further attempt can be made by re-operating the appropriate OUTGOING GROUP key followed by the LAST NUMBER REPEAT key. This causes the last number keyed out over a line in that group to be transmitted again.

The operator can decide to meter an outgoing call set up via the console. On conclusion of a metered call, the audible tone is sounded, and re-operation of the METER key causes the VDU to display the extension identity and the number of metered units recorded on that call.

The operator uses the CAnCEL key to negate the previous action; for example, if an incorrect digit has been keyed. Operation of the LAST CALL RECOVER key re-connects the last call handled to the console, providing that the call has not matured in the meantime; it is therefore possible to negate an operation of the WITHDRAW key.

The Monarch 120 system offers various call diversion facilities to extension users, including divert all calls (DAC) , divert on no reply (DNR) and divert on busy (DOB). The operator can override these diversions where appropriate, by using the RING and STEPON keys. For example, if the operator calls a free extension which has invoked DAC, the VDU will show EXTN 234, DAC, ACTION? The diversion can be overridden by operating the RING key or followed by operating the STEP-O key. In the latter case, the YDU will then show the identity of the new extension. When DNR has been invoked, diversion would normally occur after J 0 s. However, when the operator calls an extension which has invoked DNR, the diversion only occurs if and when the STEP-ON key is operated; the YDU shows the identity of the new extension, as before. Similarly, when DOB has been invoked and the extension called from the console is busy, the diversion occurs only after operation of the STEP-ON key. These facilities ensure that the operator can offer incoming callers the choice of following a call diversion, or refusing if they only wish to speak with a particular person.

Use of the EXTENSIOn STATUS key allows the operator to determine the status of any extension without changing the condition of the line; in particular, if the extension is free, the telephone is not rung.

The operator can use the TIME key to display both time and date on the YDU, these being continually updated by data transmitted over the signalling link from the central equipment.

Two slide switches are provided on the front of the console to enable the console to be switched inactive or completely powered down. Switching the console to the inactive state normally initiates night-service working for the PABX; call handling arrangements would be defined in the system data base.

When it is switched inactive, a routine of tests can be run on the console by using the CONSOLE TEST key. This flashes all the LEDs and causes the VDU to give a schematic display of the keyboard; this display is amended after successful operation of each key.

Two LEDs are provided adjacent to the VDU to indicate the arrival of urgent and non-urgent alarm messages; an audible tone is also given.

Operation of the RECEIVING ATTETION key cancels the alarm indication and causes the fault parameters to be displayed on the VDU. The operator can relay this information to the service engineer when the fault is reported. In most cases this will be sufficient to identify hardware faults down to PWB level so that the correct replacement item can be brought to site.

The MMI (man-machine interface) key changes the function of the console to that of a simple terminal which can be used to carry out system diagnosis and administration. MMI instructions are implemented by use of a range of special codes sent from the digit keypad; the VDU is extensively used in MMI to display system data. Various levels of access are provided into MMl, each requiring a password to be keyed-in prior to using the MMI facilities. The customer level is the most restricted; service and specialist levels offer increasingly sophisticated facilities. Some of the functions available at customer level are:

(a) definition of system abbreviated dialling codes,

(b) activation/deactivation of extensions,

(c) definition of extension hunting groups,

(d) displaying/resetting meter counts,

(e) revision of directory numbers,

(f) listing of extension/trunk attributes, and (g) resetting system time/date.

At the service level, some of the functions available are

(a) clearing system fault records,

(b) resetting alarms,

(c) running diagnostic tests, and (d) displaying port status.

At the specialist level, some of the functions are

(a) clearing facility statistics,

(b) setting fault analysis, and

(c) examining memory contents.

These lists are by no means exhaustive, and demonstrate that the console has wide ranging uses in the MMI mode. This avoids the expense of providing a dedicated terminal on site and allows the customer to carry out administrative tasks that would otherwise require the attendance of a service engineer. The use of MMI during system maintenance will be the subject of a later article in the Journal.

CONCLUSIONS

This article has described what is probably the world's most advanced operator's console for small PABXs.

After 4 years of development and field trials, the production and delivery of Monarch 120 consoles are now well under way; together with the central equipment units, these are being manufactured by Plessey Office Systems at Nottingham, and GEC Telecommunications (Private Systems Division) at Coventry, which are also marketing the system abroad under its earlier title of Customer Digital Switching System No. 1 (CDSSI).

Further development of the console is already under way to ensure that it continues to meet customer requirements in what is becoming an increasingly competitive and demanding area of the telecommunications business.

ACKNOWLEDGEMENTS

The author wishes to thank his colleagues in the BPO and UK Industry who have contributed to the successful development of the Monarch 120 operator's console.

References

I POTTER, A. R. Monarch 120: A new Digital PABX. POEEJ, Vol. 73, p. 14, Apr. 1980.

2 GRIFFITHS, D. F., and CARD, S. E. A ew Concept in PABX Operator's Console. lEE, Private Electronic Switching Systems Conference, Apr. 1978.

3 GRIFFITHS, D. F. Big Advance for small PABX. POTJ, Vol. 30, No.1, p. 26, Spring 1978.

4 WICKE DEN, D. K. A New 480-character Alphanumeric Electroluminescent vDU. Proceedings of the Technical Programme, r TERNEPCO ,1977.

5 VECHT, A., et 01. DC Electroluminescence in Zinc Sulphide:

State of the Art. Proceedings of the IEEE, Vol. 61, No.7, July 1973.